Impedance based anatomy generation

ABSTRACT

Methods and systems for the determination and representation of anatomy anatomical information are disclosed herein.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 14/259,384, filedApr. 23, 2014, which is a continuation of U.S. application Ser. No.13/495,541, filed Jun. 13, 2012, now U.S. Pat. No. 8,744,566, which is acontinuation of U.S. application Ser. No. 12/437,812, filed May 8, 2009,now U.S. Pat. No. 8,571,647. All subject matter set forth in the abovereferenced application is hereby incorporated by reference into thepresent application as if fully set forth herein.

TECHNICAL FIELD

This invention relates to the determination and representation ofanatomical information and/or physiological information relating to aheart using, e.g., a non-contact catheter.

BACKGROUND

Use of minimally invasive procedures, such as catheter ablation, totreat a variety of heart conditions, such as supraventricular andventricular arrhythmias, is becoming increasingly more prevalent. Suchprocedures involve the mapping of electrical activity in the heart(e.g., based on cardiac signals), such as at various locations on theendocardium surface (“cardiac mapping”), to identify the site of originof the arrhythmia followed by a targeted ablation of the site. Toperform such cardiac mapping a catheter with one or more electrodes canbe inserted into the patient's heart chamber.

Conventional 3D mapping techniques include contact mapping andnon-contact mapping. In contact mapping techniques one or more cathetersare advanced into the heart. Physiological signals resulting from theelectrical activity of the heart are acquired with one or moreelectrodes located at the catheter distal tip after determining that thetip is in stable and steady contact with the endocardium surface of aparticular heart chamber. Location and electrical activity is usuallymeasured sequentially on a point-by-point basis at about 50 to 200points on the internal surface of the heart to construct anelectro-anatomical depiction of the heart. The generated map may thenserve as the basis for deciding on a therapeutic course of action, forexample, tissue ablation, to alter the propagation of the heart'selectrical activity and to restore normal heart rhythm. On the otherhand, in non-contact-based mapping systems a multiple electrodescatheter is percutaneously placed in the heart chamber of interest. Oncein the chamber, the catheter is deployed to assume a 3D shape. Using thesignals detected by the non-contact electrodes and information onchamber anatomy and relative electrode location, the system providesphysiological information regarding the endocardium of the heartchamber.

SUMMARY

In some aspects, a method includes inserting a catheter into a heart,the catheter comprising three or more electrodes. The method alsoincludes moving the catheter to each of multiple, different positions inthe heart. The method also includes for each of the different catheterpositions, causing current to flow between at least some of theelectrodes and in response to current flow, measuring an electricalsignal at each of one or more of the electrodes. The method alsoincludes determining anatomical information about the heart based onpositions of the catheter electrodes and the measured signals at thedifferent catheter positions.

Embodiments can include one or more of the following.

The determination of the anatomical information accounts for a change inconductivity at the cardiac chamber boundary. The determination accountsfor a first conductivity inside the cardiac chamber boundary and asecond conductivity outside the cardiac chamber boundary. Determiningthe anatomical information can include determining the anatomicalinformation based at least in part on impedance information generatedbased on the measured signals at the different catheter positions. Theimpedance information is based on a conductivity contrast between bloodand surrounding tissue.

The anatomical information can include a representation of at least aportion of a boundary of the heart.

Determining the anatomical information can include detecting a boundaryof the heart. Determining the anatomical information can include, foreach of the different catheter positions, determining a surface based onthe measured signals, the surface representing a surface at which theconductivity changes. The surface can be a closed and parameterizedsurface around at least a portion of the catheter. The surface can be anellipsoid. The surface can be a curvilinear surface. The surface canprovide a boundary between a region represented by a first conductivityinside the surface and a region represented by a second conductivityoutside the surface, the first conductivity being different from thesecond conductivity.

Determining the anatomical information can include, for each of thedetermined surfaces selecting one or more regions of the surfacecorresponding to a boundary of a portion of the heart.

Selecting the one or more regions can include selecting the one or moreregions based at least in part on a distance between a portion of thesurface and the catheter. Selecting the one or more regions can includeselecting the one or more regions based at least in part on a magnitudeof a distortion field, the distortion field being based at least in parton a difference between a field calculated based on the measurements anda field in a homogonous medium. Selecting the one or more regions caninclude selecting the one or more regions based at least in part on anerror calculation in an optimization used to generate the surface.Determining the anatomical information can include joining the regionsof the determined surfaces corresponding to an expected chamber boundaryto generate the anatomical information. Joining the regions can includeusing a meshing algorithm.

The method can also include using the multiple electrodes on thecatheter to measure cardiac signals at the catheter electrodes inresponse to electrical activity in the heart.

The method can also include determining physiological information atmultiple locations of the boundary of the heart based on the determinedpositions of the catheter electrodes and the measured cardiac signals atthe different catheter positions.

The method can also include using one or more electrodes on the catheterfor delivering ablation energy for ablating tissue.

Determining the anatomical information based on the measured signalsfrom the one or more electrodes can include distinguishing electricalsignals indicative of cardiac electrical activity from those responsiveto the injected current.

The method can also include displaying at least a portion of theanatomical information. Displaying at least a portion of the anatomicalinformation can include displaying at least a portion of the boundary ofthe heart.

In some additional aspects, a method can include inserting a catheterinto a heart, the catheter comprising multiple, spatially distributedelectrodes including multiple sets of electrodes each set comprising atleast two electrodes. The method can also include for each of themultiple different sets of electrodes, causing current to flow betweenat least some of the electrodes and in response to current flow,measuring an electrical signal at each of one or more measuringelectrodes. The method can also include determining anatomicalinformation based on the measured signals.

Embodiments can include one or more of the following.

The determination of the anatomical information can account for a changein conductivity at the cardiac chamber boundary.

The determination can account for a first conductivity inside thecardiac chamber boundary and a second conductivity outside the cardiacchamber boundary.

Determining the anatomical information can include determining theanatomical information based at least in part on impedance informationgenerated based on the measured signals. The impedance information canbe based on a conductivity contrast between blood and surroundingtissue. The anatomical information can include a representation of atleast a portion of a boundary of the heart.

Determining the anatomical information can include detecting a boundaryof the heart. Determining the anatomical information can includedetermining a surface based on the measured signals, the surfacerepresenting a surface at which the conductivity value changes. Thesurface can be a closed and parameterized surface around at least aportion of the catheter. The surface can be an ellipsoid. The surfacecan be a curvilinear surface. The surface can provide a boundary betweena region represented by a first conductivity inside the surface and aregion represented by a second conductivity outside the surface, thefirst conductivity being different from the second conductivity.

Determining the anatomical information can include for each of thedetermined surfaces selecting one or more regions of the surfacecorresponding to an expected boundary of the heart. Selecting the one ormore regions can include selecting the one or more regions based atleast in part on a distance between a portion of the surface and thecatheter. Selecting the one or more regions can include selecting theone or more regions based at least in part on a magnitude of adistortion field, the distortion field being based at least in part on adifference between a field calculated based on the measurements and afield in a homogonous medium. Selecting the one or more regions caninclude selecting the one or more regions based at least in part on anerror calculation in an optimization used to generate the surface.

Determining the anatomical information can include joining the regionsof the determined surfaces corresponding to an expected chamber boundaryto generate the anatomical information. Joining the regions can includeusing a meshing algorithm.

The method can also include using the multiple electrodes on thecatheter to measure cardiac signals at the catheter electrodes inresponse to electrical activity in the heart.

The method can also include determining physiological information atmultiple locations of the boundary of the heart based on positions ofthe catheter electrodes and the measured cardiac signals. The method canalso include using one or more electrodes on the catheter for deliveringablation energy for ablating tissue.

Determining the anatomical information based on the measured signalsfrom the one or more electrodes can include distinguishing electricalsignals indicative of cardiac electrical activity from those responsiveto the injected current.

The method can also include displaying at least a portion of theanatomical information.

In some aspects, a method includes inserting a catheter into a heart,the catheter comprising three or more electrodes. The method alsoincludes causing current to flow between at least some of the electrodesand in response to current flow, measuring an electrical signal at eachof one or more of the electrodes. The method also includes determining aboundary of at least a portion of the heart based on the measuredelectrical signals. The method also includes displaying a portion ofless than the entire boundary of the heart.

Embodiments can include one or more of the following.

The method can also include measuring cardiac signals at the catheterelectrodes in response to electrical activity in the heart anddetermining physiological information at multiple locations of theboundary of the heart based the measured cardiac signals.

The method can also include displaying the physiological information atmultiple locations of the boundary of the heart.

The method can also include displaying the physiological information atmultiple locations of the boundary of the heart for only a determinedvalid area. Displaying the boundary can include displaying the boundaryfor a portion of less than all of the heart.

The determination of the boundary can accounts for a change inconductivity at the cardiac chamber boundary. The determination canaccount for a first conductivity inside the cardiac chamber boundary anda second conductivity outside the cardiac chamber boundary.

Determining the boundary can include determining the anatomicalinformation based at least in part on impedance information generatedbased on the measured signals. The impedance information can be based ona conductivity contrast between blood and surrounding tissue.

Determining the boundary can include determining a surface based on themeasured signals, the surface representing a surface at which theconductivity value changes. The surface can be a closed andparameterized surface around at least a portion of the catheter. Thesurface can provide a boundary between a region represented by a firstconductivity inside the surface and a region represented by a secondconductivity outside the surface, the first conductivity being differentfrom the second conductivity.

Determining the anatomical information can include for each of thedetermined surfaces selecting one or more regions of the surfacecorresponding to an expected boundary of the heart. Selecting the one ormore regions can include selecting the one or more regions based atleast in part on a distance between a portion of the surface and thecatheter. Selecting the one or more regions can include selecting theone or more regions based at least in part on a magnitude of adistortion field, the distortion field being based at least in part on adifference between a field calculated based on the measurements and afield in a homogonous medium. Selecting the one or more regions caninclude selecting the one or more regions based at least in part on anerror calculation in an optimization used to generate the surface.

Determining the anatomical information can include joining the regionsof the determined surfaces corresponding to an expected chamber boundaryto generate the anatomical information.

The method can also include determining a valid area of the boundary andusing a visual indicia to indicate the determined valid area of theboundary.

Displaying the portion of less than the entire boundary of the heart caninclude using a visual indicia to indicate a valid area of the boundary.

The method can also include determining a valid area of the boundary.Displaying the portion of less than the entire boundary of the heartcomprises using a visual indicia to indicate the determined valid areaof the boundary.

In some aspects, a system includes a catheter comprising one or moreelectrodes configured to inject a current and to measure electricalsignals in response to the injected current. The system also includes adevice configured to determine a position of the catheter electrodes.The system also includes a processing unit configured to determineanatomical information about the heart based on positions of thecatheter electrodes and measured electrical signals at differentcatheter positions.

Embodiments can include one or more of the following.

The processing unit can be configured to account for a change inconductivity at a cardiac chamber boundary in the determination of theanatomical information.

The processing unit can be configured to account for a firstconductivity inside the cardiac chamber boundary and a secondconductivity outside the cardiac chamber boundary.

The processing unit can be configured to determine the anatomicalinformation based at least in part on impedance information. Theimpedance information can be based on a conductivity contrast betweenblood and surrounding tissue.

The anatomical information can include a representation of at least aportion of a boundary of the heart.

The processing unit can be configured to determine the anatomicalinformation by determining a surface based on the measured signals, thesurface representing a surface at which the conductivity changes.

The processing unit can be configured to, for each of the determinedsurfaces, select one or more regions of the surface corresponding to aboundary of a portion of the heart.

The processing unit can be configured to select the one or more regionsbased at least in part on a distance between a portion of the surfaceand the electrodes.

The processing unit can be configured to select the one or more regionsbased at least in part on a magnitude of a distortion field, thedistortion field being based at least in part on a difference between afield calculated based on the measurements and a field in a homogonousmedium.

The processing unit can be configured to select the one or more regionsbased at least in part on an error calculation in an optimization usedto generate the surface.

The processing unit can be configured to join the regions of thedetermined surfaces corresponding to an expected chamber boundary togenerate the anatomical information.

The multiple electrodes can be further configured to measure cardiacsignals in response to electrical activity in the heart.

The processing unit can be configured to determine physiologicalinformation at multiple locations of the boundary of the heart based onpositions of the catheter electrodes and measured cardiac signals.

In some aspects, a system includes a catheter comprising multiple,spatially distributed electrodes including multiple sets of electrodeseach set comprising at least two electrodes, the electrodes beingconfigured to inject a current and to measure electrical signals inresponse to the injected current. The system also includes a processingunit configured to determine anatomical information about the heartbased on the measured signals.

Embodiments can include one or more of the following.

The processing unit can be configured to account for a change inconductivity at the cardiac chamber boundary in the determination of theanatomical information.

The processing unit can be configured to account for a firstconductivity inside the cardiac chamber boundary and a secondconductivity outside the cardiac chamber boundary.

The processing unit can be configured to determine the anatomicalinformation based at least in part on impedance information generatedbased on the measured signals at the different catheter positions.

The impedance information can be based on a conductivity contrastbetween blood and surrounding tissue.

The anatomical information can include a representation of at least aportion of a boundary of the heart.

The processing unit can be configured to determine the anatomicalinformation by determining a surface based on the measured signals, thesurface representing a surface at which the conductivity changes.

The processing unit can be configured to, for each of the determinedsurfaces, select one or more regions of the surface corresponding to aboundary of a portion of the heart.

The processing unit can be configured to select the one or more regionsbased at least in part on a distance between a portion of the surfaceand the catheter.

The processing unit can be configured to select the one or more regionsbased at least in part on a magnitude of a distortion field, thedistortion field being based at least in part on a difference between afield calculated based on the measurements and a field in a homogonousmedium.

The processing unit can be configured to select the one or more regionsbased at least in part on an error calculation in an optimization usedto generate the surface.

The processing unit can be configured to join the regions of thedetermined surfaces corresponding to an expected chamber boundary togenerate the anatomical information.

The electrodes on the catheter can be further configured to measurecardiac signals in response to electrical activity in the heart.

The processing unit can be configured to determine physiologicalinformation at multiple locations of the boundary of the heart based onthe determined positions of the catheter electrodes and the measuredcardiac signals.

In some aspects, a system includes a catheter that includes two or moreelectrodes configured to inject a current and to measure electricalsignals. The system also includes a processing unit configured todetermine a boundary of at least a portion of the heart based on themeasured electrical signals and a display device configured to display aportion of less than the entire boundary of the heart.

Embodiments can include one or more of the following.

The two or more electrodes can be further configured to measure cardiacsignals in response to electrical activity in the heart and theprocessing unit can be further configured to determine physiologicalinformation at multiple locations of the boundary of the heart based themeasured cardiac signals.

The display device can be further configured to display thephysiological information at multiple locations of the boundary of theheart.

The system can be configured to display the physiological information atmultiple locations of the boundary of the heart for only the determinedvalid area.

The processing unit can be configured to account for a change inconductivity at the cardiac chamber boundary in the determination of theboundary.

The processing unit can be configured to account for a firstconductivity inside the cardiac chamber boundary and a secondconductivity outside the cardiac chamber boundary.

The processing unit can be configured to determine the boundary based atleast in part on impedance information generated based on the measuredsignals at the different catheter positions.

The impedance information can be based on a conductivity contrastbetween blood and surrounding tissue.

The processing unit can be configured to determine the boundary bydetermining a surface based on the measured signals, the surfacerepresenting a surface at which the conductivity changes.

The processing unit can be configured to for each of the determinedsurfaces select one or more regions of the surface corresponding to aboundary of a portion of the heart.

The processing unit can be configured to select the one or more regionsbased at least in part on a distance between a portion of the surfaceand the catheter.

The processing unit can be configured to select the one or more regionsbased at least in part on a magnitude of a distortion field, thedistortion field being based at least in part on a difference between afield calculated based on the measurements and a field in a homogonousmedium.

The processing unit can be configured to select the one or more regionsbased at least in part on an error calculation in an optimization usedto generate the surface.

The processing unit can be configured to join the regions of thedetermined surfaces corresponding to an expected chamber boundary togenerate the anatomical information.

The two or more electrodes can be further configured to measure cardiacsignals in response to electrical activity in the heart.

The processing unit can be configured to determine physiologicalinformation at multiple locations of the boundary of the heart based onthe determined positions of the catheter electrodes and the measuredcardiac signals.

Embodiments of the system may also include devices, software,components, and/or systems to perform any features described above.

Embodiments of the methods and systems generally disclosed herein can beapplied to determining the position of any object within an organ in apatient's body such as the patient's heart, lungs, brain, or liver.

As used herein, the “position” of an object means information about oneor more of the 6 degrees of freedom that completely define the locationand orientation of a three-dimensional object in a three-dimensionalcoordinate system. For example, the position of the object can include:three independent values indicative of the coordinates of a point of theobject in a Cartesian coordinate system and three independent valuesindicative of the angles for the orientation of the object about each ofthe Cartesian axes; or any subset of such values.

As used herein, “heart cavity” means the heart and surrounding tissue.

As used herein, the “anatomical information” means information about ananatomy of an organ, information about a boundary of an organ, and/orinformation about an anatomy for ablation.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. In case of conflict withdocuments incorporated herein by reference, the present documentcontrols.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary schematic diagram of an arrangement forpositioning electrodes in a patient's heart.

FIGS. 2a-2c show perspective, end, and side views, respectively, of adeployed catheter with multiple current injection electrodes (CIE) andmultiple potential measuring electrodes (PME).

FIGS. 3A and 3B are schematic diagrams of two current injectionelectrodes (CIE) pair constellations.

FIGS. 4A-4E are schematic diagrams of a process for generatinganatomical information including a reconstructed anatomy.

FIG. 5 is a schematic diagram of a model for determining a parameterizedsurface.

FIG. 6 is a schematic diagram of a process for determining aparameterized surface.

FIG. 7 is an exemplary graph of a confidence model.

FIG. 8 is a schematic diagram of a dipole at a distance from an infiniteplane.

FIG. 9 is a schematic diagram of a partial boundary determination.

FIG. 10 is a schematic diagram of an ellipsoidal local parameterizedsurface.

FIG. 11 is a schematic diagram of a curvilinear local parameterizedsurface.

FIG. 12 is a schematic diagram of valid patches relative to a catheterlocation.

FIGS. 13A-13D show exemplary anatomical information.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Embodiments disclosed herein include a method and system for generatingpatient specific anatomical information such as cardiac anatomy. Thepatient specific cardiac anatomy can be used, for example, during thegeneration of an electroanatomical map (EAM) of heart tissue which canbe used to identify the site of origin of an arrhythmia followed by atargeted ablation of the site. While patient specific anatomy is anecessary component in the generation of an EAM for the catheterablation treatment of arrhythmia, accurate representation of cardiacanatomy is useful for other medical applications such as congestiveheart failure, injection of biologics into the heart and scar tissue,anatomical guidance of biopsies, minimally invasive valve repair andreplacement, and the like.

Embodiments disclosed herein include methods and systems for generatinganatomical information including patient specific anatomy by derivingimpedance based information from a tracked multi-electrode array (MEA)catheter. FIG. 1 shows a schematic diagram of an exemplary embodiment ofan anatomy generation system 200. The system 200 includes a moveablecatheter 210 having multiple spatially distributed electrodes (describedbelow). During the anatomy generation process, a physician or medicalprofessional 202 inserts the catheter 210 into a chamber of interest(e.g., the heart 212) of a patient 214. The catheter 210 is displaced toone or multiple locations within the chamber of interest (e.g., theheart 212). In some embodiments, the distal end of the catheter 210 isfitted with multiple electrodes spread somewhat uniformly over thecatheter (e.g., as described in more detail below). The catheter 210includes both current injection electrodes (CIE) and potential measuringelectrodes (PME). In the example of anatomy generation for the heartchamber, due to the conductivity contrast between blood and themyocardium and surrounding tissue, the measurements collected by thecatheter 210 can be analyzed to detect chamber boundary in the vicinityof the catheter 210. In order to reconstruct the chamber anatomy, system200 includes a processing unit 206 which performs operations pertainingto anatomy determination based on a location of the catheter 210 (e.g.,a location provided by a tracking system) and the measurements from theelectrodes on the catheter 210. As the tracked catheter 210 is movedinside the chamber, a partial or complete representation of the chamberanatomy is constructed. For example, a representation of the boundary ofthe chamber can be constructed. The chamber anatomy 208 can be displayedon a display device 204 which is connected to the processing unit 206.In addition, embodiments disclosed herein include methods and systemsfor generating an EAM using the generated anatomy.

In addition, embodiments disclosed herein include methods and systemsfor generating partial chamber boundary EAM. The partial chamberboundary EAM provides physiological information about a portion (e.g., aportion of less than the entire) of a chamber such as the heart. Partialchamber boundary EAM can be useful to quickly obtain an EAM in a knownarea of interest. The construction of partial EAM is enabled by theability to reconstruct the anatomy of a part of the chamber coupled withknowledge of valid and invalid zones obtained by using the disclosedimpedance scheme.

As described herein, due to the conductivity contrast between blood andthe myocardium and surrounding tissue, measurements collected bycatheter 210 located inside the heart 212 of a patient 214 can beanalyzed to detect a chamber boundary in the vicinity of the catheter212. These measurements can be used to generate anatomical informationrepresenting the anatomy of the heart. Other exemplary methods forgenerating an anatomy of the heart (or other organ) include pointcollection, ultrasound, rotational angiography, computed tomography (CT)and magnetic resonance (MR). In general, point collection is a method inwhich a tracked catheter is moved inside the heart and numerous catheterlocations are collected. Over time the outline of the heart is tracedbased on the collection of points. Exemplary drawbacks of pointcollection for generation of an anatomy can include that the process istime consuming and can suffer from limited accuracy and uncertainty.Ultrasound is a method in which a tracked intra cardiac ultrasound/echocatheter is moved inside the heart, the 2D images collected with thecatheter are segmented to identify chamber boundary and combined usingthe 3D tracking data. Exemplary drawbacks of ultrasound for generationof an anatomy can include that the process can be time consuming,segmentation is manual, and a proprietary ultrasound catheter must beintroduced into the organ solely for determining anatomy. RotationalAngiography is a method in which a contrast agent is injected intochamber of interest and a fluoroscopy c-arm is rotated to obtainvolumetric representation. Segmentation is used to detect endocardialboundary. Exemplary drawbacks of rotational angiography can include thatits use can lengthen procedure time, may suffer from limited accuracy,it can be difficult to image all chambers, and/or excessive injection ofcontrast may be toxic. When CT & MR are used, a volumetric chamberrepresentation is acquired ahead of procedure, volume segmentationprovides cardiac chamber of interest, and registration to trackingsystem is performed during procedure. Exemplary drawbacks of CT and MRcan include that the anatomy is generated prior to the procedure whichmay lead to inaccuracy in anatomy at the time of the procedure, theprocess often requires use of contrast agent, and/or not all chamberscan easily be imaged.

It is believed that generating the anatomy based on measurementscollected by a catheter located inside the heart of a patient andcalculations based on the conductivity contrast between blood and themyocardium and surrounding tissue (e.g., as described herein) canprovide one or more of the following advantages. The generation of theanatomy can be relatively fast, since a large area of the anatomy can beacquired in each heartbeat. In another example, the anatomy informationis acquired (and may be re-acquired) during the procedure as opposed tobeing acquired prior to the procedure. In another example, these methodscan provide the advantage enabling the same catheter to be used foranatomy generation, electrical reconstruction, and/or tracking.

In some embodiments, a patient specific anatomy is generated usingimpedance based information from a tracked multi-electrode array (MEA)catheter. The system includes an MEA catheter that provides mechanicalsupport for an array of current injecting electrodes (CIE) and potentialmeasuring electrodes (PME). For example, the catheter may be configuredwith multiple electrodes and used for cardiac mapping, such as describedin commonly owned patent application Ser. No. 11/451,898, entitled“NON-CONTACT CARDIAC MAPPING, INCLUDING MOVING CATHETER AND MULTI-BEATINTEGRATION” and filed Jun. 13, 2006, application Ser. No. 11/451,908,entitled “NON-CONTACT CARDIAC MAPPING, INCLUDING PREPROCESSING” andfiled Jun. 13, 2006, application Ser. No. 11/451,871 entitled“NON-CONTACT CARDIAC MAPPING, INCLUDING RESOLUTION MAP” and filed Jun.13, 2006, and application Ser. No. 11/672,562 entitled “IMPEDANCEREGISTRATION AND CATHETER TRACKING” and filed Feb. 8, 2007, the contentsof each of which are incorporated herein by reference. The system alsoincludes electronics for driving current and measuring potential, atracking system that provides 3D location of catheter electrodes, and acomputer with appropriate software algorithm to collect data and processthe data in order to construct a 3D representation of the chamberanatomy.

The MEA Catheter

The MEA catheter can be normally introduced through a femoral vein orartery and advanced into the heart through the vascular system. The MEAcatheter has a multitude of electrodes that deploy into a threedimensional shape. For example, the MEA catheter may have 64 electrodesand deploy into a relatively spherical shape with a diameter of about 2cm. The MEA catheter may be used to collect cardiac signals, trackingsignals, as well as to generate and collect the signals necessarydetermining anatomical information such as the boundary of an organ suchas the heart.

To generate the excitation pattern necessary for anatomy construction, asequence of linearly independent current injection patterns aregenerated by utilizing current injecting electrodes (“CIE”) on thecatheter. Simultaneously potential measurement is performed on potentialmeasuring electrodes (“PME”), also mounted on the catheter. It should benoted that PME and CIE may be one and the same.

FIGS. 2a-c show different views for one embodiment of the catheter 110,which includes a base sleeve 112, a central retractable inner member114, and multiple splines 116 connected to base sleeve 112 at one endand inner member 114 at the other end. When inner member 114 is in anextended configuration (not shown), splines 116 are pulled tight to theinner member so that catheter 110 has a narrow profile for guiding itthrough blood vessels. When inner member 114 is retracted (as shown inFIGS. 2a-b ), splines 116 are deployed and pushed into an outward“olive” shaped configuration for use in the heart cavity. As explainedin more detail below, the splines 116 each carry electrodes, so when theinner member is in the retracted configuration, the electrode aredeployed in the sense that they are distributed over a greater volume.

A number (>6) of current injecting electrodes (CIE) are mounted oncatheter 110. For example, 3 orthogonal CIE pairs may be mounted on thecatheter.

The CIE are designated 119, while electrodes 118 are used as potentialmeasuring electrodes (PME). The purpose of the CIEs is to inject currentinto the heart cavity. For example, each CIE pair can define a sourceand sink electrode, respectively, for injecting current into the heartcavity.

It should be noted that any low impedance electrode can be used forcurrent injection and in a case where many or all electrodes are capableof injecting current the designation of such electrodes as CIE on thecatheter only indicates that these electrodes are actually being usedfor current injection. It should be further appreciated that otherconfiguration sets of CIE are possible as long as these configurationsare known and can be accounted for. Examples of such configurationscould be quadruples involving 4 CIE, or even a non-symmetricalconfiguration involving 3 CIE in known positions on the catheter. Forsimplicity the method of using electrode pairs will be explained, butthe same method can be applied using other configurations.

It should be appreciated that configurations other than orthogonal pairsmay be used for either method, and that more than 2 CIE may participatein current injection at a given time. FIGS. 3A and 3B show two differentCIE pair constellations. FIG. 3B shows the 3 pair constellationdescribed above while FIG. 3A shows 7 pairs. The 7 pairs are the same 3,plus 4 additional diagonal pairs.

Electronics

The MEA catheter is connected to electronics hardware capable of drivingthe necessary current and detecting both signals originating from theheart as well as those used for anatomy construction. There is a need todistinguish between the two signals in order to separate the signalbeing used for the anatomy determination from the cardiac signal. TheCIE are therefore coupled to electronics injecting the current at afrequency higher than cardiac activation (cardiac activation<2 kHz,CIE>4 kHz, e.g. 5 kHz) such that the two types of signals can be easilydistinguished using frequency analysis. It should be noted that othermethods for distinguishing between the CIE signal and the cardiacactivation signal can be used, such as injecting a spread-spectrumsignal having a low energy level in the frequency range of the cardiacactivation signal, and detecting this spread-spectrum signal in thesignal collected by the all PME.

A multitude of separate known configurations of CIE need to injectcurrent in order to interrogate the medium. There is a need to determinethe source of the injected signal and to trace it to a specific CIEconfiguration. For example, 3 pairs of CIE can inject the currentsequentially, one pair at a time, so that it is possible to trace thesource of the measured PME signals to a specific pair. This is calledtime division multiplexing. In the case of time division multiplexing,CIE are activated in sequence such that at one point in time one pair isactivated and at the next point in time another pair is activated. Theswitching between pairs may occur every cycle (e.g., ⅕ kHz=200 μs) orevery few cycles (e.g., 20 cycles, 20×200 .μs=4 mS). It should be notedthat frequency or code division (spread spectrum) multiplexing, ratherthan time division may be used to separate the signals emanating fromdifferent CIE pairs. In the case of frequency multiplexing all CIE pairsmay inject the current at the same time, but each pair uses a differentcarrier frequency. The signal collected at the PME is filtered accordingto the frequency, and the signal measured in each frequency is thenassociated with the appropriate originating pair.

The amount of current injected needs to be large enough to provide areasonable signal to noise ratio, while also small enough not tostimulate cardiac tissue. A current level of 50 μA at 5 kHz is believedto be appropriate.

Tracking System

In order to combine information collected from multiple catheterlocations, the MEA electrode locations are tracked relative to thecardiac chamber in three dimensional space. This task is accomplished bya tracking subsystem. Such subsystems have been shown previously and mayinclude any of a magnetic, impedance, x-ray and ultrasound subsystems.For example, the tracking system can be a tracking system such asdescribed in commonly owned patent application Ser. No. 12/061,297,entitled “Intracardiac Tracking System” and filed Apr. 2, 2008, thecontents of which is incorporated herein by reference.

In case of impedance tracking the tracking signals may be multiplexedonto the same medium either by a time division multiplexing scheme wheretime slots are added specifically for tracking, or using frequencydivision multiplexing by modulating the tracking signals on a differentfrequency. In some cases the same CIE pairs may be used simultaneouslyfor tracking and anatomy construction thereby not adding time slotsbeyond those necessary for tracking.

Data Processing

The system includes software for processing data collected by the MEAcatheter and tracking system to generate anatomical information such asa chamber anatomy or representation of a boundary of the chamber.

Referring to FIGS. 4A-4D, a process for generating anatomicalinformation such as a chamber anatomy is shown. In general, when thecatheter is in the heart, the signals measured by the PME are differentfrom that of the homogenous case, that is, when the entire domain isfilled with blood. These differences carry the particular informationabout the inhomogeneous distribution of the material property due to theanatomical features around the catheter. This impedance characterizationdoes not gather reliable information from great distances due to thesmoothing effect of the Laplace's equation which governs potentialdistribution in the medium: the injected current will not diffusesubstantially into regions far from the catheter. As such, the systemgenerates information about local anatomical features by detecting andrecognizing differences based on the inhomogeneous distribution. Inorder to reconstruct the entire chamber anatomy, the catheter is movedaround the chamber's interior and the impedance characterization isrepeated in several locations. Finally, the collected local anatomicalinformation belonging to the different locations is merged to form theanatomy of the entire chamber.

FIG. 4A shows a schematic description of true chamber boundary 250, asingle catheter 254 and a local parameterized surface 252 reconstructedfrom the single catheter position. The local parameterized surface 252is generated based on measurements collected by the PME on catheter 254.As described above, impedance characterization does not gatherinformation from great distances and therefore the local parameterizedsurface 254 provides only a portion of the chamber anatomy. Moreparticularly, since a single catheter location cannot detect the entirechamber anatomy, the local parameterized surface 242 is a surface thatprovides a best fit to PME measurements at a particular catheterlocation (e.g., as described in more detail below). As shown in FIG. 4B,after the local surface 252 is generated for a particular catheterlocation, the system detects and marks regions of the localparameterized surface 252 that are valid. Valid regions of the localsurface 252 are region(s) that are expected to lie on the true chamberboundary 250. These regions are detected and marked as valid patches(e.g., patches 256 a and 256 b). As shown in FIG. 4C, the catheter 254is then moved to another location (e.g., moved from location 258 a tolocation 258 b) and the process of construction of local anatomy anddetection of valid patches is repeated. As shown in FIG. 4C, the systemdetects another valid patch 256 c based on the information collected bycatheter 254 at location 258 b. As shown in FIG. 4D, to reconstruct theentire chamber anatomy or portion of interest (e.g., a portion of thechamber anatomy, but not the entire chamber anatomy), the catheter ismoved to multiple locations, using the tracking system for positioninformation in each location. At each location, the system detectsadditional valid patches corresponding to additional region(s) that areexpected to lie on the true chamber boundary 250. As shown in FIG. 4E,once the catheter has been moved around the entire chamber or theportion of interest, the chamber boundary 260 is reconstructed byconnecting the valid patches. In some embodiments, the valid patches canbe connected using a surface meshing algorithm such as the algorithmdescribed in U.S. Pat. No. 6,226,542, the contents of which are herebyincorporated by reference.

Cardiac contraction changes the anatomy of the chamber. For that reason,in some embodiments, the anatomy generation is gated according to thecardiac cycle. Gating information can be obtained from electricalmeasurements of the cardiac cycle (e.g., by the use of surface ECG orintracardiac signal from a stable location) and triggering on a constantmarker in the cardiac phase (e.g., using an R-wave detection algorithm,a threshold criterion, a maximum criterion or correlation to atemplate). Another option is to use a measurement that is affecteddirectly by the mechanical movement of the heart, such as themeasurement of the impedance between CIE, and triggering on a constantmarker in the cycle. Once a trigger is determined, the cardiac cycle isdivided into m slices (e.g., m=10), and the mentioned process isrepeated for each slice separately. Alternatively, a particular slice ofinterest may be chosen (e.g., end diastole) and other data is notcollected and/or is discarded. It is also important to note that all CIEsets may be scanned quickly enough (e.g., 4 mS) such that it can beassumed that the heart did not move substantially in that period.

Though sinusoidal signals are used to modulate the signal such that itdoes not interfere with cardiac signal, the frequency is relatively low,and so the validity of the quasi-static approximation via the Laplace'sequation remains intact:∇·(σ+jωϵ)∇ϕ=0  (Eq. 1)

Where ϕ describes the electric potential field, σ is the conductivity, ϵis the permittivity and ω is the angular frequency.

Inverse Problem Approach

The anatomical information provides a three dimensional distribution ofthe electrical conductivity of the surrounding media. The goal of thealgorithm is to find the location and orientation of the internalboundary of the heart chamber, that is, to find the boundary where theconductivity value changes from the value associated with blood. Forexample, on average the conductivity contrast between blood σ_(b) andsurrounding tissue σ_(s) is σ_(b)/σ_(s)=2.5. Theoretically, an impedancetomography technique, which is able to provide the distribution of theconductivity surrounding the medium, could be used to detect theanatomical features. However, due to the smoothing effect of current'sdistribution in material as governed by Laplace's equation, impedancetomography techniques provide blurry representation of the medium andtherefore are not ideal for the anatomy reconstruction process. Forexample the impedance tomography techniques often employ a Tikhonovregularization operator as part of the inverse solution forconductivity. This type of regularization promotes limited change inelectrical conductivity over a neighborhood and therefore contributes tothe blurriness of the final representation. In general, regularizationtechniques in inverse problems usually introduce extra equations orterms, which express a priory expectation about the solution and at thesame time mathematically convert the underlying equation system fromunderdetermined to over determined, thereby making it solvable. In otherwords, regularization techniques are needed in inverse problems tohandle the overly high number of unknown degrees of freedom, which isused to represent the conductivity distribution.

Instead of using an overly high number of degrees of freedom, in someembodiments the abrupt conductivity distribution is represented in a waythat uses only a few parameters. For example, as shown in FIG. 5, thiscan be achieved by an explicit representation of a closed andparameterized local surface 276 around the catheter 278. Thisrepresentation divides the 3D space into two regions 274 and 272. Theregion 274 in which the catheter 278 is located is associated with theconductivity of blood (Ω_(blood)) while the outside region 272 isassociated with an unknown conductivity (Ω_(external)) since it variesfrom patient to patient and between different regions in the cardiacchamber. This local parameterized surface 276 and the conductivityvalues (Ω_(blood) and Ω_(external)) constitute a local forward modelused in the inverse solver. This model aims to reconstruct the shape andvalue of the conductivity distribution. This inverse problem isnonlinear and requires the use of an iterative solver. The inversesolver is an optimizer that determines both the surface's parameters aswell as the unknown external conductivity (Ω_(external)). The choice ofthe local parameterized surface 276 is only limited by its number ofparameters or degrees of freedom. For example, a fully parameterized 3Dellipsoid introduces nine degrees of freedom: three axial parameters andsix parameters for rigid body translation and rotation. It is alsopossible to use polynomial representation, Bezier, NURBS or curvilinearfinite elements to represent the parameterized surface 276.

FIG. 6 shows a system and method for generation of a local parameterizedsurface including the measurement hardware 284 along with the inversesolver 290 (e.g., software) which reconstructs the local parameterizedsurface 276.

The measurement hardware 284 is connected to a catheter 280 placedwithin a patient's heart 282. The measurement hardware 284 collectspotential measurements and electrode location 286 from the catheter 280.The inverse solver 290 uses these potential measurements and electrodelocation information 286 in the determination of the local parameterizedsurface.

The inverse solver 290 utilizes a search algorithm in theparameter-domain in order to minimize the difference between themeasured electrode-potentials (e.g., potential measurements 286)provided by the measurement hardware 284 and the estimates of theelectric potential field 296, provided by the local forward model 288.These later samples are taken at the corresponding locations of themeasuring electrodes on catheter 280. An exemplary minimization equationis shown below:

$\min\limits_{\underset{\_}{p}\;}{{\underset{\_}{u} - {\underset{\_}{\phi}( \underset{\_}{p} )}}}_{2}^{2}$

Where p is the vector of measured electrode potentials 286, ϕ is thevector of potential samples predicted by the forward model 296 anddependent on p, which is the vector of various parameters of the forwardmodel 288 itself. During the measurement phase it is assumed thatneither the location nor the orientation of the catheter is changingsignificantly, therefore the local forward model 288 assumes steadyposition and orientation of the catheter 280. Both the measuredpotentials 286 and predicted potential values 296 can be arranged instructured vectors and so the measure of difference can be defined bythe sum of squares of corresponding differences. Minimization problemsof this type can be efficiently solved by the Levenberg-Marquardt (LM)method (e.g., using LM optimizer 294). The LM algorithm is formulated interms of the residual vector and the first derivative of this vector,which is called the Jacobian. During the search for the optimalparameter values, the forward solver 292 repeatedly solves for the everchanging local forward model 288. The solution of the forward model 288is governed by the Laplace's equation and provides the potentialdistribution for the domain defined by the local forward model 288, andso the potential values at the electrodes of the model-catheter as well.Different approximation methods such as Spherical Harmonics, FiniteElements, Boundary Elements or Multiple MultiPoles can be used todiscretize Laplace's equation, resulting in an algebraic linear equationsystem in Equation 2.Kx=f  (Equation 2)

The solution of the linear equation system provides the values for theso called degree of freedoms (x), which in turn along with thecorresponding field approximation functions constitute the overallapproximation of the electrical field. K is the so called stiffnessmatrix collecting the contribution from the discretized differentialoperator, f represents excitation due to sources or boundary conditions.

The LM algorithm requires the derivatives of the residual vector interms of the parameters of the local forward model. There are twopossible approaches to obtaining the derivatives. They can be estimatedusing finite differentiation techniques, or using a directdifferentiation method in the forward solver. In testing the directapproach was shown to be superior in terms of speed and accuracy due tothe larger approximation error of the finite differentiation technique.

Valid Patch Selection

After successful optimization of the local parameterized surface 276,the local parameterized surface 276 is expected to be similar orpartially similar to a portion of the true chamber boundary (e.g., asshown above in FIGS. 4A-4E). The region of the local parameterizedsurface that approximates the chamber boundary with sufficient accuracyis described herein as a valid patch. The rest of the localparameterized surface bears no significant influence on the electricfield-pattern predicted by the local forward model. Such surface regionsmay be present in a relatively distant location from the catheterbecause, as explained earlier, the injected current pattern will notdiffuse sufficiently into those far regions and so the field patternwill not be influenced by features located in those regions.

The parts of the local parameterized surface that are less likely toapproximate the true chamber boundary are filtered out so only the validpatches remain that are most responsible for the field pattern measuredby the electrodes and reconstructed by the optimized local forwardmodel. The final boundary of the chamber is reconstructed by forming asurface (e.g., a triangular-mesh based surface) so that it fits the setof previously obtained valid patches while also maintaining reasonablesurface-smoothness properties.

The selection of the valid patches can be a mostly a heuristicprocedure. In some embodiments, the local parameterized surface issubdivided and only certain regions are kept for the finalreconstruction step as valid patches. The main criterion for selectingthe valid patches is based on the strength of a distortion field. Thedistortion field is the difference between the field in presence ofinhomogeneity and the field which corresponds to the homogenous medium.The higher the strength of the distortion field on a certain location ofthe local parameterized surface, the more the field pattern resulting onthe PME is sensitive to the location and orientation of that surfacelocation. Therefore, the distortion field strength is believed to be agood indicator of the surface location's validity (strength ofinfluence). The main criterion is then simply to select patches thatexhibit higher distortion field than a certain threshold(df_(threshold)). This criterion is then combined with additionalside-criteria in order to increase the certainty of the decision. Insome embodiments, two side-criteria are used: one criteria is based onthe distance of the surface location from the center of the catheter,and the other criteria is based on the final residual error of the LMoptimization. It should be noted that additional quantities may alsocontribute to the accuracy of the filtering process. The side criteriaare formulated and combined via the fuzzy logic approach.

FIG. 7 shows an exemplary graph 300 of “Membership functions” of“confidence” in which the x-axis 304 represents the distance or residualwhile the y-axis 302 represents the confidence that can be used whichcan be represented by:

${C( {x,t,\alpha} )} = \frac{1}{1 + e^{\alpha{({x - t})}}}$

Where t and α are parameters of the membership function; t is theturn-point 306 and α determines the slope of the membership function atthe turnpoint 306.

After proper normalization of the quantities involved in the sidecriteria, the evaluation of the membership functions result inconfidence factors for each criterion (C_(residual) and C_(distance)).These factors are then used as multipliers of the distortion fieldstrength (df) in the final acceptance criterion for valid patchselection:df×C _(residual) ×C _(distance) >df _(threshold)  (Equation 3)

Once the above criterion is satisfied for a surface location, thesurface location will become a candidate for selection for a validpatch. The final set of surface locations is limited as well, thereforeonly those locations providing highest values for the left hand side areselected for the final reconstruction.

The LM residual is expected to be smaller when the optimization is moresuccessful and therefore the local parameterized surface is expected toapproximate the chamber boundary better. For this reason, smaller valuesfor the LM residual should produce higher confidence levels: one orclose to one. Increasing residual, on the other hand, should eventuallyswitch the corresponding confidence level down to zero. In order toestablish what “small” is, the LM residual is normalized. Thisnormalization is such that when the local forward model is thehomogenous case, the corresponding normalized residual would be exactlyone. In other words, the residual measures how much the distortion fieldis reconstructed by the optimized local forward model at the PMEcompared to the homogenous case, which is regarded as complete lack ofreconstruction. The normalization described here is only the first stepto make sure the membership function produces meaningful confidencelevels. The missing additive is the parameter of the membership functionitself, called turn-point. In some examples, for the LM residual aturn-point 306 of 0.05 is believed to be adequate. This is thenormalized LM residual value, which produces confidence level of exactlyone half. The appropriate α for this criteria is believed to be 80.

As shown in FIG. 8, similar deductions can be given for the confidencelevel generated by the distance of the surface location relative to thecatheter. For this criterion confidence should decrease as distance fromthe center of the catheter is increased. The surface location distanceis normalized by expressing it relative to the radius of the catheter.For example, a reasonable turn-point is believed to be two times thecatheter radius. For example, an appropriate α for this criteria isbelieved to be 0.5.

The threshold value in the selection criterion for the distortion fieldis derived from the analytical solution of a simple but relevantarrangement in order to account for possibly different catheter/dipoledimensions. The arrangement, as shown in FIG. 8, provides a dipole 312with moment d assumed to be a distance 314 of two times the moment dfrom an infinite plane 310. The threshold value is set to be five timesthe value measured on the plane at point v, 316. The conductivity ratiobetween the side 318 of the plane where the dipole resides and the otherside 320 of the plane is assumed to be 2.5.

For the subdivision of the local parameterized surface a surfacetriangulation is used as a mesh. The mesh is as uniform as possible, andthe average size of the triangles should match the desired resolutionfor the filtering step. In some embodiments, an average edge length of 2mm was found to be sufficient in balancing run-time with accuracy. Othersubdivision of the local parameterized surface could also be used.

Electro-Anatomical Map (“EAM’) Construction

The construction of electro-anatomical maps (EAMs) is a valuable toolfor the diagnosis and therapy of a variety of cardiac related conditionsincluding congestive heart failure, valve failure and arrhythmia. Forthe catheter ablation treatment of arrhythmia the reconstruction ofanatomy provides both an understanding of the anatomical structure aswell as the chamber boundary on which the three dimensional EAM map isconstructed.

Full Chamber Map

The chamber boundary reconstructed using impedance measurementsdisclosed herein can be used as the surface onto which electricalinformation is projected. This electrical information may be collectedusing a contact scheme or non-contact scheme (e.g., as described in U.S.Pat. No. 7,505,810, the contents of which are hereby incorporated byreference). In the case of a non-contact scheme, both electrical andanatomical data may be collected simultaneously by the MEA catheter thusexpediting the EAM generation process. Electrical information displayedon the EAM can include any of a number of isopotentials, bipolar maps,local activation time, voltage map, dominant frequency map, and thelike.

Partial Chamber EAM Map

In some applications, it is necessary to construct only a partial EAM ofthe chamber (e.g., construct an EAM of less than the entire chamber).That is, to save procedure time, only a portion of the chamber known toparticipate in the arrhythmogenic mechanism needs to be provided on theEAM. For example, in the case of scar related ventricular tachycardia,only the scarred area and its immediate surrounding tissue may berequired for clinical treatment. Such portion can represent under 25% oftotal chamber area and be collected with a limited number of catheterlocations. For example, less than 10 catheter locations may be used togenerate the partial EAM (e.g., 8 catheter locations or less, 6 catheterlocations or less, 5 catheter locations or less, 4 catheter locations).In such case, as shown in FIG. 9, it is possible to construct a partialanatomy 336 by meshing a closed surface around the valid patches (e.g.,patches 332 a, 332 b, and 332 c). Since the surface 336 is not completein this case, such closed mesh also contains areas 334 where no validpatches exist nearby. However, those are known from the valid patchselection process described above and marked invalid. Invalid areas 334in the mesh can be either transparent or rendered differently (e.g. showonly mesh edges and render mesh faces transparent, display gray, makesemi-transparent).

Once the partial chamber anatomy is constructed, electrical informationcan then be displayed only on the valid areas (e.g., area 336) of theanatomy using either a non-contact or contact scheme. It is important tonote that the added information of valid and invalid zones is crucial tothe construction of a partial EAM map. If invalid areas of the anatomyare not marked as such, the EAM may lead to wrong clinicalinterpretation. The information regarding the validity of the mapprovided with the impedance scheme is unavailable with other pointcollection schemes making partial maps more difficult to interpret.

Experimental Results

FIGS. 10 and 11 show exemplary local parameterized surfaces. Moreparticularly, FIG. 10 shows an ellipsoidal local parameterized surfacewith 9 degrees of freedom while FIG. 11 shows a curvilinear localparameterized surface with 18 degrees of freedom.

FIG. 12 shows valid patches detected relative to a catheter location.

FIGS. 13A-D, provides multiple projections of an experimentreconstructing left ventricular (“LV”) anatomy. FIG. 13A provides athree dimensional representation of the reconstructed anatomy of the LV,FIG. 13B provides a two dimensional representation of the reconstructedanatomy of FIG. 13A in the x-y plane, FIG. 13C provides a twodimensional representation of the reconstructed anatomy of FIG. 13A inthe x-z plane, and FIG. 13D provides a two dimensional representation ofthe reconstructed anatomy of FIG. 13A in the y-z plane. The constructionof the anatomy was accomplished using a MEA catheter with 6 CIE and 64PME in a constellation similar to the one shown in FIG. 3. The catheterwas moved to 51 locations within the left ventrical (LV). The syntheticmeasurements were generated using a Finite Element Method simulator. Asshown in the figures, even areas that were sparsely sampled by thecatheter are reasonably reconstructed.

Other Embodiments

In some aspects, the catheter used to generate the anatomicalinformation and/or generate the EAM information can additionally includean electrode for delivering ablation energy for ablating tissue. Assuch, a single catheter can generate an EAM map (including generatingthe anatomical information used for the EAM map) and perform ablation ofidentified regions of the organ. It is believed that this can providethe advantage of limiting the number of catheters inserted into theorgan of the patient. For example, an ablation procedure can involvemapping of electrical activity in the heart (e.g., based on cardiacsignals), such as at various locations on the endocardium surface(“cardiac mapping”), to identify the site of origin of the arrhythmiafollowed by a targeted ablation of the site. A single catheter insertedinto the patient's heart chamber can be used both to perform suchcardiac mapping (including generating the anatomy of the heart) and toperform the ablation.

It should be understood that while this disclosure describes use ofcurrent injection and potential measurement, it is also possible toimpart a known voltage on active electrodes and measure resultantpotential or current. In effect, any interrogation of the mediumperformed by active electrodes which results in a current being diffusedinto the medium and a potential field imparted on it should be viewedand one and the same.

It should further be understood that while this invention describes theuse of conductivity contrast, an impedance contrast comprising of boththe conductivity contrast and/or permittivity contrast can also be used.In this case both the amplitude and phase or I and Q components of thepotential measured by the PME may be used by the same algorithm. Ratherthan estimating the conductivity alone, the complex impedance havingboth conductivity and/or permittivity can be computed. As the carrierfrequency of the injected current is increased it is expected thatpermittivity contrast will increase and accounting for and usingimpedance contrast rather than conductivity alone is believed to improveaccuracy.

The methods and systems described herein are not limited to a particularhardware or software configuration, and may find applicability in manycomputing or processing environments. The methods and systems can beimplemented in hardware, or a combination of hardware and software,and/or can be implemented from commercially available modulesapplications and devices. Where the implementation of the systems andmethods described herein is at least partly based on use ofmicroprocessors, the methods and systems can be implemented in one ormore computer programs, where a computer program can be understood toinclude one or more processor executable instructions. The computerprogram(s) can execute on one or more programmable processors, and canbe stored on one or more storage medium readable by the processor(including volatile and non-volatile memory and/or storage elements),one or more input devices, and/or one or more output devices. Theprocessor thus can access one or more input devices to obtain inputdata, and can access one or more output devices to communicate outputdata. The input and/or output devices can include one or more of thefollowing: Random Access Memory (RAM), Redundant Array of IndependentDisks (RAID), floppy drive, CD, DVD, magnetic disk, internal hard drive,external hard drive, memory stick, or other storage device capable ofbeing accessed by a processor as provided herein, where suchaforementioned examples are not exhaustive, and are for illustration andnot limitation.

The computer program(s) can be implemented using one or more high levelprocedural or object-oriented programming languages to communicate witha computer system; however, the program(s) can be implemented inassembly or machine language, if desired. The language can be compiledor interpreted. The device(s) or computer systems that integrate withthe processor(s) can include, for example, a personal computer(s),workstation (e.g., Sun, HP), personal digital assistant (PDA), handhelddevice such as cellular telephone, laptop, handheld, or another devicecapable of being integrated with a processor(s) that can operate asprovided herein. Accordingly, the devices provided herein are notexhaustive and are provided for illustration and not limitation.

References to “a microprocessor” and “a processor”, or “themicroprocessor” and “the processor,” can be understood to include one ormore microprocessors that can communicate in a stand-alone and/or adistributed environment(s), and can thus be configured to communicatevia wired or wireless communications with other processors, where suchone or more processor can be configured to operate on one or moreprocessor-controlled devices that can be similar or different devices.Furthermore, references to memory, unless otherwise specified, caninclude one or more processor-readable and accessible memory elementsand/or components that can be internal to the processor-controlleddevice, external to the processor-controlled device, and can be accessedvia a wired or wireless network using a variety of communicationsprotocols, and unless otherwise specified, can be arranged to include acombination of external and internal memory devices, where such memorycan be contiguous and/or partitioned based on the application.Accordingly, references to a database can be understood to include oneor more memory associations, where such references can includecommercially available database products (e.g., SQL, Informix, Oracle)and also proprietary databases, and may also include other structuresfor associating memory such as links, queues, graphs, trees, with suchstructures provided for illustration and not limitation.

Accordingly, other embodiments are within the scope of the followingclaims. Various modifications and additions can be made to the exemplaryembodiments discussed without departing from the scope of the presentinvention. For example, while the embodiments described above refer toparticular features, the scope of this invention also includesembodiments having different combinations of features and embodimentsthat do not include all of the described features. Accordingly, thescope of the present invention is intended to embrace all suchalternatives, modifications, and variations as fall within the scope ofthe claims, together with all equivalents thereof.

We claim:
 1. A method comprising: inserting a catheter into a heart, thecatheter comprising three or more electrodes; causing the catheter tomove to each of multiple, different positions in the heart; for each ofthe multiple, different positions, causing current flow between at leastsome of the three or more electrodes and measuring electrical signals,from the current flow, at each of one or more of the three or moreelectrodes; determining anatomical information about the heart bydetecting surface boundaries of the heart based at least in part onimpedance information generated based on the measured electricalsignals; and determining at least one of: one or more distances betweendifferent surface boundaries of the heart, and one or more distancesbetween at least one of the three or more electrodes and at least one ofthe surface boundaries of the heart.
 2. The method of claim 1,comprising: displaying the one or more distances between the differentsurface boundaries of the heart.
 3. The method of claim 1, comprising:displaying the one or more distances between the at least one of thethree or more electrodes and the at least one of the surface boundariesof the heart.
 4. The method of claim 1, wherein the impedanceinformation comprises complex impedance information determined from themeasured signals.
 5. The method of claim 1, wherein the impedanceinformation is based on at least one of a conductivity contrast and apermittivity contrast between homogenous and non-homogenous media. 6.The method of claim 1, wherein the impedance information is based on atleast one of a conductivity contrast and a permittivity contrast betweenblood and surrounding tissue.
 7. The method of claim 1, wherein theanatomical information accounts for a change in conductivity at acardiac chamber boundary of the surface boundaries with a firstconductivity inside the cardiac chamber boundary and a secondconductivity outside the cardiac chamber boundary, the firstconductivity being different from the second conductivity.
 8. The methodof claim 1, wherein the anatomical information accounts for a change inpermittivity at a cardiac chamber boundary of the surface boundarieswith a first permittivity inside the cardiac chamber boundary and asecond permittivity outside the cardiac chamber boundary, the firstpermittivity being different from the second permittivity.
 9. The methodof claim 1, wherein detecting the surface boundaries of the heartcomprises determining a closed and parameterized surface around at leasta portion of the catheter based on the measured electrical signals, thesurface boundaries representing boundaries at which at least one of aconductivity and a permittivity changes.
 10. The method of claim 1,wherein detecting the surface boundaries of the heart comprisesdetecting the surface boundaries of the heart based at least in part ona magnitude of a distortion field based at least in part on a differencebetween a field calculated based on the measured electrical signals anda field in a homogenous medium.
 11. A method comprising: inserting acatheter into a heart, the catheter comprising multiple, spatiallydistributed electrodes including multiple sets of electrodes, each setcomprising at least two electrodes; for each of the multiple differentsets of electrodes, causing current to flow between at least some of theelectrodes and in response to current flow, measuring an electricalsignal at each of one or more measuring electrodes; determininganatomical information about the heart by detecting surfaces of theheart based at least in part on complex impedance information generatedbased on the measured signals; and determining at least one of adistance between different surfaces of the heart, and a distance betweenone of the electrodes and one of the surfaces of the heart.
 12. Themethod of claim 11, comprising at least one of; displaying the distancebetween the different surfaces of the heart; and displaying the distancebetween the one of the electrodes and the one of the surfaces of theheart.
 13. The method of claim 11, wherein the complex impedanceinformation is based on at least one of a conductivity contrast and apermittivity contrast between homogenous and non-homogenous media. 14.The method of claim 11, wherein the complex impedance information isbased on at least one of a conductivity contrast and a permittivitycontrast between blood and surrounding tissue.
 15. The method of claim11, wherein determining the anatomical information comprises:distinguishing signals indicative of cardiac electrical activity fromthe measured signals based on the current flow; and determining theanatomical information based on the measured signals based on thecurrent flow.
 16. A system comprising: a catheter comprising three ormore electrodes configured to inject a current and to measure electricalsignals in response to the injected current; and a processing unitconfigured to determine anatomical information about the heart bydetecting surfaces of the heart based at least in part on impedanceinformation generated based on the measured signals, wherein theprocessing unit determines at least one of: one or more distancesbetween different surfaces of the heart, and one or more distancesbetween at least one of the three or more electrodes and at least one ofthe surfaces of the heart.
 17. The system of claim 16, wherein theanatomical information accounts for a change in conductivity at acardiac chamber boundary with a first conductivity inside the cardiacchamber boundary and a second conductivity outside the cardiac chamberboundary, the first conductivity being different from the secondconductivity.
 18. The system of claim 16, wherein the anatomicalinformation accounts for a change in permittivity at a cardiac chamberboundary with a first permittivity inside the cardiac chamber boundaryand a second permittivity outside the cardiac chamber boundary, thefirst permittivity being different from the second permittivity.
 19. Thesystem of claim 16, wherein the impedance information comprises compleximpedance information determined from the measured signals and thecomplex impedance information is based on at least one of a conductivitycontrast and a permittivity contrast between at least one of: homogenousand non-homogenous media, and blood and surrounding tissue.
 20. Thesystem of claim 16, wherein the electrodes on the catheter areconfigured to measure cardiac signals in response to electrical activityin the heart and the processing unit is configured to determinephysiological information at multiple locations on the surfaces of theheart based on the determined positions of the electrodes and themeasured cardiac signals.